152 



insload of 2 dnys as in the han^in<j drop nicthod. .many 

 problems williin the physiology of the tissues can he in- 

 vestigated under mueli hetler conditions. It was found Ihal 

 the growth of the tissues j)roceed at a constant rale for 2- .T 

 weeks and the increase of the tissues is expressed in a, 

 parabola when the medium is a nutrient. In a protective 

 medium the growth is exi)ressed by an S-shaped ciu've. 

 The S-siia|)ed curve indicates the residual activity of a tissue. 

 The activity of a tissue at a given instant, is a function of 

 at least three independent variables, the inherent cell activity, 

 and the concentration of growth-activating and growth-inhi- 

 biting substances in the medium. The inherent activity of a 

 tissue is its activity in a protective medium without nutrient 

 material. 



This inherent growth energy of tissues has been tho 

 subject for si)ecial investigations by ('arrel''^). There is 

 a definite relation between the growth energy of a given 

 tissue and its age, and it is found by earlier stu(hes of 

 Carrel that the healing of an aseptic wound is a function of 

 the age of the ])atient. which is determined by the size of 

 the wound and its index of cicatrization, (d u N o ii y) '-"). 



Pure strains of fibroblasts or heart tissue were according 

 to Carre 1, placed in the culture flask of the D type and 

 the culture medium was composed of a solid phase ,0,5 cc. 

 of plasma and IV2 cc. of Tyrode solution containing 5 'Vo 

 embryonic tissue juice) and the liquid phase of Tyrode 

 solution only. The residual life of a fragment of heart of 

 an 8 days embryo varied from 7 — 12 days. The residual 

 life of a fragment of an 11 year old strain of fibroblasts, 

 lasted 7 — 8 days. In comparing the residual growth energy 

 of a heart fragment from a 10 days old chicken embryo and 

 a 17 days old embryo, the grow^th of the older tissue was 

 about 30 per cent less extensive than that of Ihe young(>r 

 one. 



By the method of cultivating tissues in flasks uninter- 

 ruptedly for long periods of time. Carrel and l''l)eling 



