78 I^UE\ Ijy or 1\\ JJRTEBRATE,'^ 



vae in sterile saline with small losses for a period of 

 6 weeks, after which time the animals were sacrificed for 

 chemical analysis. In sterile nutrient solutions the larvae 

 stayed alive, as mentioned above, for many months. 



In the light of such experiences, the data of Table 11 

 ought to be used only with great caution. Different mi- 

 crobial floras will develop depending on whether the 

 worms are kept aerobically or anaerobically and the in- 

 fluence of various bacteria on the worms may vary wide- 

 ly. One of the problems for future investigation is, there- 

 fore, that of the survival of helminths under varying 

 oxygen tensions in sterile nutrient media. The experi- 

 ments summarized in Table 11 are sufficient in the 

 writer's opinion to demonstrate that most of the worms 

 investigated show a decided resistance to lack of oxygen. 

 Further conclusions can be draw^n only with reserve and 

 only if corroborated by other evidence. 



Besides the above data some further facts are known 

 concerning the anaerobic relationship's of helminth eggs 

 and larvae. Many observations indicate conclusively that 

 the eggs of a number of nematodes withstand anaerobic 

 conditions exceedingly well. The eggs of Ancylostoma, 

 Parascaris, Ascaris, Trichocephalus and Nematodirus 

 are not easily damaged by lack of oxygen. They can be 

 kept, without losing their viability, for days or even 

 weeks under anoxic conditions (Looss, 1911; Bataillon, 

 1910 ; Zawadowski, 1916 ; Faure-Fremiet, 1913 ; Zawadow- 

 ski and Orlow, 1927 ; Zviaginzev, 1934 ; Dinnik and Dinnik, 

 1937; Cram and Hicks, 1944). In all cases, however, the 

 development of the eggs ceases sooner or later, to be re- 

 sumed only when oxygen again becomes available. 



The details seem to vary with different species. In 

 Parascaris, only maturation, fertilization and probably 

 the first cleavage stages are possible under anaerobic 

 conditions (Faure-Fremiet, 1913; Szweikowska, 1929; 

 Dyrdowska, 1931). In Oxyuris equi development con- 



