Continuing the ontogenetic-phylogenetic parallel related 

 above, Pavlov stated that the fetus is at first similar to the 

 infusoria, not only in organization, but also in the character 

 of nutrition. The infusorian extracts food and oxygen from 

 drops of water in the mouth. At the beginning the fetus is 

 constructed quite simply; it has the shape of a vesicle, 

 devoid of any organs and composed of gelatin C"does not 

 this structure simulate the organic infusoria?" Pavlov asked). 

 The source of food and water for the fetus is an insignifi- 

 cantly small portion of the transparent amniotic fluid. When 

 natural development moves upward from plants to animals, the 

 digestive canal acquires great importance. In general, it is 

 considered the first special organ. Digestion is the first 

 function necessary for the continuation of existence. "Does 

 not the same occur in the fetus?" Development of the fetal 

 digestive canal is gradual; hence it is impossible that 

 digestion develops suddenly. Pavlov suggested that the 

 digestive canal in the early fetus is insufficiently developed 

 and for this reason cannot accomplish its function. He noted 

 that nobody doubted that the digestive canal in polyps, 

 radiates, and insects can digest food. The developing fetus, 

 according to his analysis, behaves as those animals do; why 

 then does its digestive canal not function? As in higher 

 animals the organs of digestion appear more perfected, so in 

 the fetus the digestive system improves in the process of 

 development. 



Between the twelfth and sixteenth weeks, when, according 

 to Pavlov, metamorphosis ends, the amniotic fluid provides 

 insufficient food and oxygen to meet the requirements of the 

 fetus. "Therefore nature seeks new means to complete the 

 deficiency, and thus the placenta is formed" ($ 134). Between 

 the fetus and the mother there is a juice, richer in nutritional 

 substances than the amniotic fluid, which is extracted by the 

 vessels of the umbilical canal. 



Pavlov's third chapter, on human fetal nutrition, includes 

 the assumptions which partially form his dissertation's 

 conclusions. In summary, these include: 1) "All that is living 

 is from fluid" (Thesis 1); 2) "Fetal life can be divided into 

 two stages — the stage of metamorphosis and the stage of 

 perfection" [Thesis 111); 3) The method of embryonic changes 

 in nutrition repeats the changes in the transition from lower 

 animals ("infusoria") to higher animals. 



171 



