202 HUMAN BIOLOGY 



The first is that the egg is fertihzed by a sperm carrying 

 one X chromosome so that an individual results which has 

 two X chromosomes and is a female. The second is that the 

 egg is fertilized by a sperm with no x chromosome, so that 

 the resulting individual possesses only the one x chromosome 

 contained in the egg and is therefore a male. 



The determination of sex is, however, not so simple as it 

 appears to be from these equations. Many factors enter in to 

 modify the process which we do not understand. Some of 

 them may be environmental and nutritional. Gradations 

 between maleness and femaleness occur and some individuals 

 may be both, that is hermaphrodites. Though the chromo- 

 somes may contain the physical basis of heredity we are 

 profoundly ignorant as to what it actually is. Modern chem- 

 istry does not enhghten us on this point. Inheritance of 

 some characters through the cytoplasm of the egg is a 

 possibiHty that has been much discussed. 



THE SCIENCE OF CYTOLOGY 



The science which deals with cells is called appropriately 

 cytology. The cytologist is concerned with the smallest 

 visible things, the astronomer with the largest. Yet in a sense 

 this science stands at the head of the hst because it is a 

 kind of superstructure built upon the other sciences, which 

 are said to be more fundamental. The cytologist must 

 avail himself of advances in the more easily studied fields 

 of physics and chemistry, but in doing so he has to b^ very 

 cautious because there is always the question as to how far 

 discoveries in these sciences may be applied in the inter- 

 pretation of vital processes occurring largely out of his 

 reach in living cells. But the reverse does not hold; the 

 physicist and the chemist may, and often do, forge right 

 ahead in their researches without taking into consideration 

 in the least the activities of living matter. It is almost 

 invariably dead material, the reactions of which are more 

 definitely predictable, to which they give exclusive attention. 



Cytology is also the meeting place or the center of integra- 

 tion of related sciences. The biologist and the bacteriologist, 

 the physiologist and the pathologist all contribute material 

 of the utmost importance to our knowledge of cells. Evidently 



