Townsend (1935) has described the egg of Synthesiomyia nudiseta and recorded the interesting fact that the larva forms a cocoon. The larval stages and the puparium do not appear to have been described. That this species was not among the larvae of some unknown muscids described by Banks (1912) is evident from the figures of the-posterior spiracles. The present communication provides an account of all the early stages.

1. A new species of the genus Rhabditis is described.

2. The development of a standard method of culturing the species is outlined, and the effect on the nematode of varying the method of culturing is detailed and discussed.

3. The relationships between the nematode and the bacteria and Protozoa of the cultures are discussed.

The writer wishes to express his deep gratitude to Prof. A. D. Hobson, for his invaluable advice and assistance at all stages. Thanks are also due to King's College, the University of Durham, for financial assistance in the form of a Post-Graduate Studentship.

1. The osmotic pressure of the medium in which the nematodes were cultured has been shown to be equivalent to that of about 30 mM. NaCl.

2. The effects of immersion in a saline solution isotonic with the above, in glass-distilled water, and in hypertonic saline solutions, have been described. Particular attention was paid to changes in the length of the body, in the appearance and behaviour of the alimentary canal, and in the movement of the body.

3. The results obtained have been discussed, and the following tentative conclusions reached:

(a) The main aqueous exchanges occur through the cuticle and protoplasm covering the periphery of the body, and are controlled by the protoplasm rather than by the cuticle. The cuticle thus does not act as aja impermeable outer covering which insulates the animal from its environment.

(b) The species normally lives in an environment which is hypotonic to the body fluids, and maintains its internal osmotic pressure by means of an active method of osmotic regulation. The alimentary canal is probably partially, but not wholly, responsible for this regulation.

(c) Swelling occurs in distilled water because the removal of water in the initial stages is not rapid enough to cope with the extra inflow. Later the excess water is removed.

(d) In concentrated solutions, water is removed from the body, and the internal osmotic pressure may also be increased to some extent by the penetration of osmotically active substances to the body, through the cuticle and hypodermis of the body wall. Penetration through the hypodermis is slower than through the cuticle.

(e) During recovery in concentrated solutions, there is a slow removal of osmotically active material from the body. The hypertrophy of the lateral and post-anal organs, which sometimes occurs under these conditions, may be connected with this removal.

1. The homonym Styphlodora compactum Dawes, 1941, has been renamed S. compressa.

2. Several suggestions have been made regarding the invalidity of proposed species of the genus Styphlodora. S. compactum Byrd, Parker & Reiber, 1940, should be regarded as a synonym of S. bascaniensis Goldberger, 1911, S. natricis as a synonym of S. magna Byrd & Denton, 1938, S. agkistrodontis as a synonym of S. floridanis Byrd, Parker & Reiber, 1940, S. lachesidis as a synonym of S. horridum (Leidy, 1850).

3. A suggestion has been made to relegate the proposed genus Paurophyllum Byrd, Parker & Reiber, 1940, to synonymity with the genus Styphlodora Looss, 1899. The proposed new species Paurophyllum simplexus and P. megametricus Byrd, Parker & Reiber, 1940, are identical and should be known as Styphlodora simplexa (Byrd, Parker & Reiber, 1940a) n.comb. S. aspina Byrd, Parker & Reiber, 1940, is a synonym of this species.

4. A revised key to the sixteen apparently valid species of the genus Styphlodora has been constructed. S. floridanis and S. simplexa have been found places in it provisionally, though it is suggested that further study of the trematode parasites of the kidney of Agkistrodon piscivorus might result in the merging of these species into a single species, namely, Styphlodora simplexa (Byrd, Parker & Reiber, 1940).

A turkey brought to this laboratory for examination in 1934 was found to be harbouring protozoal parasites in the red blood cells, but the parasite was not definitely identified at the time. The parasite was determined as a Plasmodium species by Mr R. Daubney when he returned from leave; and when Dr Carlton Herman was a guest worker at thia Institute in 1939 Mr Daubney suggested that he might like to investigate the incidence of this particular parasite in turkeys in the neighbourhood of Kabete. A visit was then made to a nearby turkey farm, and blood smears taken from many poults. One of these birds proved to be infected with a Plasmodium. Using the blood of this bird, experimental infection was set up in other young turkeys.

Using the method developed by VanOrden & Nelson (1926) in withdrawing and examining cloacal contents of four captive individuals of the Plathander or clawed frog (Xenopus laevis), the writer determined that infections of ciliate protozoans had persisted for more than 6 years.

1. An analysis has been made of the numbers and location of adult female Sarcoptes scabiei found on 886 men suffering from scabies

2. The average number of mites per man was 11·3. 52% of the cases had under six mites and only 3·6% over fifty.

3. 63% of the mites were found on the hands and wrists, 10·9% on the elbows, 9·2% on the feet, 8·4% on the genitals and 4% on the buttocks.

4. So-called ‘severe’ cases of scabies, showing widespread clinical symptoms, may have very few parasites, whereas cases with few symptoms may have large mite populations.

A preliminary report on the results of our studies on the comparative efficacy of different culicifuges under laboratory conditions has been published (Roy, Ghosh & Chopra, 1942).

The genus Eulaelaps was raised by Antonio Berlese in 1903 to include the species of Laelaptidae in which the genito-ventral scutum of the female was large and extended to the anal scutum, and which possessed a large triangular meta-podal scutum posterior to coxa iv.

The fertility rate of eggs of the tick, Ornithodorus moubata, was investigated with the following results:

(1) Although three batches of eggs can be laid after a single mating, fertility is considerably improved if a fresh mating take place before each oviposition.

(2) Fertility of the eggs decreases with the interval between mating and oviposition (the latter takes place usually only after a blood meal).

(3) If the organ of Géné is faulty (permanently everted) none of the eggs will develop.

(4) Eggs have a wide tolerance of temperature, and show no alteration in fertility rate from 22 to 32° C. At 34° C. no larvae are produced at all.

(5) Females lay over twice as many eggs in sand as they do on a flat surface such as filter paper.

In this review we have given an account of the various methods which are available to determine the size of virus particles. In § IV we have endeavoured to bring the ultrafiltration method into agreement with other methods by suggesting a different factor for converting pore size to virus size from the factors commonly used. Throughout we have recognized the probability that most viruses are hydrated in solution and have distinguished between the size and molecular weight in solution and the size and molecular weight when dried.

In § VII we have given formulae suitable for interpreting centrifugation and diffusion data when the possibility of hydration is contemplated.

It is evident that this complication, added to that of shape, makes it necessary for several measurements by different methods to be made before one can claim to know the size of a virus. For this reason, only in the cases of three viruses have we thought the data sufficiently adequate to enable the size and shape and molecular weight of the Virus, both dry and hydrated, to be stated. These three viruses, tobacco mosaic, tomato bushy stunt and vaccinia respectively, are separately discussed in § X.

It will be clear from the preceding sections that, while the position regarding our knowledge of the absolute sizes of viruses is far from satisfactory, there has been amassed a large amount of data bearing on this subject. We should, however, point out that we have found it necessary to select what we consider to be the best experimental data in some cases and that there may be conflicting ideas expressed by various authorities. Frampton (1942) has studied the electron microscope photographs published by Stanley & Anderson (1941) and Anderson & Stanley (1941) and arrives at an entirely different estimate of the length of tobacco mosaic virus. Kausche, Pfankuch & Ruska (1939) reported one value for the length of this virus which is approximately half that given by Stanley & Anderson. Electron photomicrographs published by von Ardenne (1940) and Holmes (1941) for what are probably strains of the same virus, also suggest that the values given should not be taken as absolute. Frampton (1939 a, b), on the basis of diffusion and viscosity experiments and the stream birefringence of this virus, has suggested previously that it forms a gel at any concentration and therefore cannot be said to have a size. Lauffer (1940) has given reasons for supposing this argument to be incorrect. Bernal & Fankuchen (1941a) have discussed the possibility of tobacco mosaic virus particles being shorter than the value taken from Kausche et al. (1939) and conclude that in the plant itself the particle may be as short as 100 mμ.

In obtaining values of size arid shape from electron microscope data we have made the assumptions, which may not be correct, that long, thin viruses shrink in width rather than in length on drying and that almost spherical viruses contract approximately evenly in all directions. At the moment there would seem to be no method of proving or disproving the truth of these assumptions, but we believe it unlikely that drying will result in such a gross change in shape that it would invalidate our calculations. For instance, in the case of haemocyanin from Helix pomatia, it seems improbable that, on drying, an already anhydrous ellipsoidal molecule of 66 × 15·32 mμ would contract in length and expand in-width to form a sphere of some 24 mμ diameter.

In our treatment of hydration we have found it necessary to regard the density and volume of ‘bound’ water as being the same as that of water in bulk, which may not be entirely true. However, we regard the total volume occupied by water in cases of great hydration, as shown by tomato bushy stunt virus, as being not markedly smaller than that of the same mass of free water. It is, nevertheless, a well-established fact that in certain cases, gelatin for example (Svedberg, 1924), a small contraction in volume does take place when dry protein is added to water. This phenomenon does not, however, necessitate the assumption that the water of hydration, is denser than ordinary water, and can be explained in other ways.

The viscosity of solutions of viruses, especially the rod-shaped plant viruses, has attracted much attention as a method of finding frictional and axial ratios of viruses (Frampton, 1939 a, b; Lauffer, 1938; Loring, 1938; Neurath, Cooper, Sharp, Taylor, Beard & Beard, 1941; Kobinson, 1939 a, b; Stanley, 1939), but, in addition to the lack of experimental verification of the formulae used, in many cases (Robinson, 1939 a, b; Frampton, 1939 a, b) the formulae have been applied to experimental results obtained in circumstances which exclude the fundamental postulates on which the formulae are based. For this reason we have omitted a detailed discussion of such methods.

It would appear that in order to obtain evidence as to the size of a virus it is desirable to study the virus in as purified a form as possible and also to show that when ‘homo-geneous’ preparations are obtained, they do not consist merely of macromolecular substances contaminated with a small quantity of virus. Furthermore it is desirable to obtain at least sufficient data to enable one to assess both size and shape of the particles rather than to assume some shape or some density value which may be incorrect.