EXISTING ORGANISMS— PHYSIOLOGY 99 



Quantitative studies of the precipitates produced in these reac- 

 tions serve as a measure of finer degrees of relationship, but all 

 tests are subject to modification by various conditions. The 

 following excerpts from Nuttall's work are a partial consideration 

 of these factors. 



He writes: "Uhlenhuth agrees with me in finding that the zoologi- 

 cal relationships between animals are best demonstrated by means of 

 powerful antisera. He judged from reactions with such antisera 

 that the ox is not so closely allied to the sheep, as the sheep is to 

 the goat. He found that weak anti-sheep serum produced no 

 reaction in ox blood. In my paper of 21, XI. 1901, I wrote 'The 

 more powerful the antiserum the greater is its sphere of action upon 

 the bloods of related species'. For instance, a weak anti-human 

 serum produced no reaction with the blood of the Hapalidae, 

 whereas a powerful antiserum did produce a reaction and proved 

 what I may be permitted to call the 'blood relationship' in the 

 absence of a better expression. ... I also noted that reactions 

 took place 'to a lesser extent in the bloods of allied animals, than 

 in the homologous blood.' " In the following paragraph he shows 

 that the serum may react with a remotely related antiserum if 

 allowed to stand for some time, but he notes the facts that have 

 been brought out here, "that anti-mammalian sera only produce 

 these later reactions in mammalian bloods, anti-avian sera simi- 

 larly in avian sera alone." 



Reproduction. Finally, the reproductive processes of organ- 

 isms afford unsurpassed evidence of relationship. Many cells 

 retain the property throughout their lives; others are formed as 

 end products in the highly specialized organisms and normally 

 lose it. Some cells of the latter type are capable, however, under 

 the stimulus of abnormal conditions in the organism, of repro- 

 ducing during the process of regeneration of tissues or parts even 

 though reproduction is not a constant function. A degree of 

 specialization which completely eliminates this function is rela- 

 tively rare. 



Amitosis. In its simplest state cell reproduction apparently 

 consists of a simple elongation, constriction, and separation of the 

 parent cell, resulting in the production of two daughter cells. This 

 process is known as amitosis. It occurs in certain parts of metazoa, 

 as for example the well-known laboratory illustration, the ovary 

 of the cricket, apparently in highly specialized cells. 



