44 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



oocytes, which later disappear. Fibroblasts and capillaries may grow into 

 blood clots and organize them, and connective tissue cells may penetrate also 

 into wounds or into necrotic areas in the cartilage. Some collections of lympho- 

 cytes around blood vessels or around the perichondrium and some increase in 

 the connective tissue in the transplanted fat tissue in autogenous transplants 

 may later disappear. 



In the guinea pig as in the rat, homoiogenous cartilage may survive at least 

 for as long as almost six months, and probably permanently, although slight 

 degenerative changes or, in places, complete necrosis may take place in the 

 intercellular cartilage substance in the course of the first or second week. 

 During the second and third weeks, the lymphocytic infiltration may become 

 quite marked, although this varies in different cases and even in different 

 places in the same transplant. In some instances, towards the end of the third 

 week, the lymphocytes may be so numerous that the cartilage becomes se- 

 questered. During this time, also, the connective-tissue growth continues, lead- 

 ing either to a thickening of the septa in the fat tissue or to a substitution of 

 fat tissue by fibrous tissue. In the second week, epithelioid and giant cells 

 develop fairly often in the fat tissue and frequently perichondrial cartilage is 

 formed around necrotic cartilage. It is of interest that in all the species ex- 

 amined so far, mitoses are rarely found in perichondrial tissue and in young 

 cartilage cells, and only once was a mitosis seen in a perichondrial cell in the 

 guinea pig. During the fourth week the homoiogenous reaction is fully de- 

 veloped. Not only may newly-formed cartilage surround the necrotic area, but 

 also connective tissue with lymphocytes, with or without blood capillaries, 

 or lymphocytes without connective tissue may penetrate a necrotic area in 

 the cartilage and replace it. Lymphocytes may infiltrate and destroy part of 

 the perichondrium, but they penetrate the hyaline intercellular cartilage sub- 

 stance not at all, or merely for a short distance. They do not destroy healthy 

 cartilage to any large extent. On the other hand, cellular cartilage may more 

 readily be invaded by lymphocytes and, at least in part, be destroyed. But on the 

 whole the lymphocytic infiltration in cartilage- fat transplants is moderate and 

 it is found especially around the living cartilage, in places where dense fibrous 

 tissue surrounds cartilage or perichondrium ; but there may be much lympho- 

 cytic infiltration also in preserved fat and areolar tissue. During the second 

 month conditions are similar and lymphocytes may now also move lengthwise 

 in the direction of the fibrillation in the cartilaginous ground substance and 

 here they gradually perish. The injurious action of the lymphocytes makes it 

 occasionally possible for the blood vessels and connective tissue cells to pene- 

 trate for a short distance the marginal portion of the cartilage. Otherwise, 

 connective tissue cells push only into necrotic cartilage. After 5^2 months, the 

 reaction on the part of the host cells was not more intense than at earlier 

 periods and the lymphocytic reaction over wide areas could be mild ; likewise, 

 some fat and areolar tissue could still be preserved. The homoiogenous bone 

 marrow had become necrotic and was replaced by a loose fibrillar connective 

 tissue ; bone was surrounded in places by giant cells. 



In general, in homoiogenous thyroid and fat tissue the activities of the con- 





