172 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Nematohelminthes. 



Development of Nematodes.*— Andre Martin has made an interesting 

 study of the conditions of development in parasitic Nematodes. His 

 experiments show that the development, hatching and survival of the 

 egg and embryo of the parasitic Nematodes of mammals and birds, are 

 dependent on physical and chemical factors of the environment, and on 

 the physical and chemical properties of the ovular envelopes. Temper- 

 ature exerts a preponderating influence. Development is accelerated 

 in proportion as the temperature rises, up to a limit beyond which it does 

 not take place. This limit varies for the different parasites. The 

 embryo of some Nematodes (Ascaris equorum, Ascaris canis, Tricho- 

 cephalus depressiusculus, Sclerostomes, Ankylostomes) develop rapidly in 

 the temperature of their host or one approximating to it. The embryos 

 of Ascaris vitulorum, Ascaris suis, and Heterakis columbse are never 

 formed at 38°, but if the temperature be lowered to 33° development 

 becomes possible, and the embryo is built up in a few days. The ova of 

 these last three parasites show a remarkable sensitiveness to a temperature 

 of 38°. Segmentation begins, but is arrested at the stage of a morula with 

 large blastomeres (Ascaris of the calf), with two blastomeres (Ascaris of 

 the pig), or with small blastomeres (Heterakis). This degree of temper- 

 ature exercises an inhibitory influence on the ovum and the capacity for 

 development disappears, not returning even when the ova are transferred 

 to a temperature of 33°. Conversely, if ova in process of development 

 in a temperature of 33° be transferred to 38°, segmentation is at once 

 arrested and embryos are not formed. This sensitiveness to a tempera- 

 tnre of 38° is a physiological character of these forms. At moderate 

 temperatures of the external environment development is always 

 possible, but it is very slow. The formation of the embryo in certain 

 parasites requires several months even in the most favourable environ- 

 ment. At low temperatures the ovum is indifferent to the substances in 

 solution in the medium, with the exception of gas. When the tempera- 

 ture rises to 33° and 38° the segmentation presents peculiarities due to 

 the substances in solution in the medium ; it is sometimes accelerated, 

 sometimes retarded, both acceleration and retardation being due to 

 metallic ions in the solutions. Hydrochloric acid, chloride of sodium, 

 bicarbonate and carbonate of sodium, chloride of potassium, hasten 

 development ; chloride of calcium and chloride of magnesium retard it. 

 Acceleration and retardation vary according to the parasites. They are 

 greater for the Ascaris of the calf than for that of the horse. The salts 

 show an antagonism to one another, as can be seen from the variations 

 in the duration of the development, and of the survival of the embryo. 

 The degree of concentration is of little importance ; effects are only 

 shown when there is a degree much greater than the ova are apt to en- 

 counter in the conditions of natural development. The eggs of Ascaris 

 vitulorum and of Ascaris equorum develop in water, the temperature of 

 the laboratory and at 33°. Free oxygen is indispensable to the develop- 

 ment of the embryo of most oviparous Nematodes ; without it, segmenta- 

 tion does not take place. But this need for free oxygen must diminish 



* Ann. Sci. Nat., xviii. (1913) pp. 1-151. 



