1. The eggs of Nematodirus filicollis when laid contain an embryo with seven or eight cells, they pass out of the infested host with the faeces.

2. Even under favourable conditions development takes place slowly and the embryos are not ready to hatch until 24–28 days have elapsed. In their early stages the embryos are not able to withstand desiccation and are killed if frozen or subjected to high temperatures.

3. Whilst still within the egg-shell the embryo undergoes two ecdyses and when ready to hatch is enclosed in a tightly fitting sheath formed by the incompletely cast skin of the second moult; the larvae on liberation from the egg-shell are therefore in a more advanced condition than those of most other Strongylids (e.g. Haemonchus or Anchylostoma) and are in a stage comparable with that reached by the latter at the end of their period of free existence.

4. The sheathed larvae are often retained for a long time within the egg-shells and both in this position and after hatching can resist complete desiccation for considerable periods (twenty months or even longer); when dried they are able to withstand freezing as well as temperatures much above those likely to be met with in the open.

5. The free larvae will live for a considerable time in water, they possess well-developed migratory instincts and climb vertical surfaces, such as grass stems and blades, and the glass walls of the vessels in which they are kept.

6. The sheaths are cast off by the larvae when these are subjected to temperatures approximating to the blood-temperature of the host; completion of the second moult occasionally also takes place at laboratory temperatures under certain abnormal conditions.

7. No infection experiments were made on sheep, but other evidence shows that these animals must become infected by swallowing the sheathed larvae, either when free or whilst still enclosed in the eggshells.

8. A number of young stages of the parasite were met with in the intestines of sheep, the smallest of these being only little more advanced in structure than the larvae just after ecdysis.

This paper is written with the purpose of drawing further attention to the value of the complement fixation reaction as a diagnostic test in dourine and of recommending a method of procedure and technique arrived at with an experience of 15,000 tests for dourine made at the Veterinary Research Laboratory, Lethbridge.

During an investigation extending over several years of the forms of Trypanosoma lewisi, as met with in naturally infected Mus decumanus, I have met with many phases which I have not seen described.

That ticks are a very serious trouble in countries where stock forms the basis of the wealth of the country is too well known to require elaborate demonstration, for the fact that they are the agents of transmission of some of the most fatal and devastating diseases is now generally recognised by the stock-farmer.

All of our guinea-pigs infected with Trypanosoma brucei (strain “ferox”) died whether they were treated or not. It is evident that both tryposafrol and novo-tryposafrol exerted a directly injurious effect upon the guinea-pigs. Reckoning the day on which the guinea-pigs were inoculated as day 1, the 19 treated guinea-pigs died respectively on days 5, 6, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 11, 18, 19, 19, 26, 27 and 33. The six untreated guinea-pigs died respectively on days 23, 25, 25, 27, 44 and 45. The two preparations of the dye are therefore worse than useless as remedies for Nagana in guinea-pigs.

Five dogs were infected with Piroplasma canis (Cambridge strain) of which four were treated and one not treated with novo-tryposafrol.

All of the dogs died although treatment was given under the most favourable conditions, starting on the day of inoculation. The four treated dogs died on days 12, 9, 17 and 12 after inoculation respectively; the untreated (control) dog died on the 13th day. The drug exerted no influence upon the course of the disease, nor upon the appearance of the parasites and their progressive increase in the blood. Novo-tryposafrol may therefore be regarded as useless in the treatment of canine piroplasmosis, and, judged from these results on dogs, it will no doubt prove to be equally useless in the treatment of bovine piroplasmosis when it has received a scientific trial in competent hands.

In view of the negative results obtained by ourselves and other independent investigators, working especially with trypanosomiasis, we conclude that the value of tryposafrol or novo-tryposafrol as a remedy for any of the diseases enumerated by the authors is open to grave doubt since the chief claims as to its efficacy were based on experimental results which the authors state that they obtained with Nagana.