The Cellular Basis 173 



i 

 physiologically and developmentally. The most delicate of all 



tests are physiological, as is shown by the Weidal test in typhoid 

 fever, the Wassermann reaction in syphilis, the reactions of im- 

 munized animals to different toxins, etc. Lillie has recently 

 shown that egg cells give off a substance which he calls "fertil- 

 izing which can be detected only by the way in which spermato- 

 zoa react to it. No chemical or physical test can distinguish be- 

 tween the different eggs or spermatozoa produced by the same 

 individual, but the reactions of these cells in development prove 

 that they are different. Undoubtedly chemical and physical dif- 

 ferences are here present but no chemical methods at present 

 available are sufficiently delicate to detect them. 



It is one of the marvelous facts of biology that practically 

 every sexually produced individual is unique, the first and last 

 of its identical kind, and although some of these individual dif- 

 ferences are due to varying environment, others are evidently due 

 to germinal differences, so that we must conclude that every 

 fertilized egg cell differs in some respects from every other one. 



But are there molecules and atoms enough in a tiny germ cell, 

 such as a spermatozoon, to allow for all these differences? Mie- 

 scher has shown that a molecule of albumin with 40 carbon atoms 

 may have as many as one billion stereo-isomers, and in protoplasm 

 there are many kinds of albumin and other proteins, some with 

 probably more than 700 carbon atoms- In such a complex sub- 

 stance as protoplasm the possible variations in molecular con- 

 stitution must be well nigh infinite, and it can not be objected on 

 this ground that it is chemically and physically impossible to 

 have as many varieties of germ cells as there are different kinds 

 of individuals in the world. 



Permutation's of Chromosomes. Even with regard to morpho- 

 logical elements which may be seen with the microscope it can be 

 shown that an enormous number of permutations is possible (Fig. 

 58). It seems probable, as Boveri has shown, that different 

 chromosomes of the fertilized egg differ in hereditary potencies, 



