CHEMISTRY OF THE CELL NUCLEUS 199 



but in all individuals of any particular species of animal or 

 plant, though differing in number in different species. The 

 equal halving of each chromosome which occurs during 

 mitosis maintains this numerical constancy except in a certain 

 period of the life history of each individual, and this period 

 occurs in the formation of the reproductive cells ; here 

 accompanying the atypical or heterotype mitosis just mentioned, 

 half of the number of chromosomes is thrown out, and the act 

 of fertilisation consists in a fusion of the male and female 

 germ cells ; each parental nucleus provides half the normal 

 number of chromosomes, and thus the fertilised egg-cell starts 

 with the full complement once more. Many biologists regard 

 the chromosomes as the actual bearers of the characters 

 which an organism inherits from its parents, or at any rate 

 this view is adopted as a working hypothesis and places the 

 transmission of characters from parent to offspring upon a 

 material foundation. 



We thus see that observations on the nucleus form not 

 only one of the most fascinating of microscopic studies, but 

 that they open up all the vexed problems of the meaning and 

 mechanism of heredity. It is even possible that the abnormal 

 course mitosis pursues in cancerous and other tumours may 

 explain, at any rate in part, their malignancy, and every step 

 in the knowledge of cancer is important to the practical 

 physician as well as to the unfortunate man or woman who 

 happens to fall a victim to this fell disease. 



I do not intend, however, to follow the subject further 

 along any of these interesting lines, for the main purport of 

 this essay is the more prosaic, though perhaps not less useful 

 one of setting down certain advances which have been made 

 in the chemical knowledge of the structures we have been 

 mentioning. Many gaps still exist in our knowledge, but they 

 are less numerous now than they were twenty or even ten 

 years ago, so prolific and fruitful has the work of chemical 

 physiologists and pathologists been during the last decade. 

 I am not alone in believing that chemistry will play an 

 important share in elucidating the secrets of that mysterious 

 and fatal ailment cancer, to which allusion has already been 

 made. 



But before I can take up the question of nuclear chemistry, 

 there is another function of the nucleus, not second in value 



