TISSUE CULTURE 83 



he has added insuUn, hemm, cysteine, and thyroxin. These 

 last three substances were chosen because each of them contains 

 an important element; hemin contains iron; cysteine, sulphur; 

 and thyroxin, iodine. Each of these substances is important 

 for growth. 



Again and again we find reason to regard protein as the 

 fundamental substance which underlies life. Salts, carbo- 

 hydrates, and fats will keep the living machine going, but to 

 make new protoplasm a protein base is needed. 



Every problem in cell physiology would be elucidated, at 

 least to a degree, if subjected to study by the technique of 

 tissue culture. Several such problems have been mentioned. 

 In addition, there are such purely physical ones as the viscous, 

 elastic, and glutinous state of protoplasm and the mechanism 

 underlying chromosome migration. Then there are physiological 

 (if not also philosophical) problems, such as the nature of death. 

 Strangeways, in order to illustrate to his students that there are 

 two types of death, that of the body as a whole and of the indi- 

 vidual cell, was wont to purchase fresh sausage at the market 

 and from its ground meat make a number of cultures of which 

 one or two always formed thriving colonies of cells. In the 

 Carrel laboratories, growth in culture has been obtained from 

 fragments of tissue kept for five or six days in cold storage. 



Of great importance is the problem of the healing of wounds. 

 If Carrel could, from studies on the influence of substances 

 on the rate of growth of cells in culture, hasten the rate of 

 reparation of tissue ten times, a cutaneous wound would heal 

 in less than twenty-four hours, and a fracture of the leg would 

 be mended in four or five days. Experiments by Lecomte du 

 Noiiy have shown that the rate of cicatrization (healing) of a 

 sterile wound is a function not only of the area of the wound 

 but also of the age of the patient ; that is to say, the area of 

 the wound being the same, the rate of repair is faster in young 

 individuals than in old. Later work by Carrel, Ebeling, and 

 Baker demonstrated that these findings may be explained on 

 the basis of progressive chemical changes which take place in the 

 blood plasma during the lifetime of the individual, in other words, 

 age. Parker demonstrated a marked difference in the action 

 of infant and adult serums on colonies of fibroblasts from sub- 

 cutaneous human tissue. One-half of them were treated with 



