72 FRANKLIN P. MALL 



growth of tissues, as revealed by Harrison's method, we can 

 understand a Uttle better the process of dissociation. In fact 

 we have in our collection two striking examples of tissue culture 

 in human embryos. In one, the cells had formed an irregular 

 mass which is growing actively, but the contour of the organs 

 has been entirely lost. In the other, from a tubal pregnancy, 

 for some unknown reason, the ovum had been completely broken 

 into two parts, which in turn had cracked the embryo, and from 

 each piece had been a vigorous independent tissue growth, or, 

 as we may now say, a tissue culture. Accordingly, when an 

 embryo through changed environment is profoundly affected, 

 the development of one part of the body may be arrested, while 

 the remaining portion may continue to grow and develop in 

 an irregular manner. In very young embryos tissues or even 

 entire organs become disintegrated, as can easily be recognized 

 by the cytolysis and histolysis present, and the resultant dis- 

 organized tissue cannot continue to produce the normal form 

 of an embryo. If this process is sharply localized, for instance, 

 in a portion of the spinal cord or in the brain, spina bifida or an- 

 encephaly results. To produce a striking result, as in cyclopia, 

 a small portion of the brain must be affected at the critical time, 

 and I think the work of Stockard has shown clearly that this 

 is before the eye primordia can be seen. Consequently, in 

 order to produce a human monster, which is to live until the 

 end of gestation, the altered environment must be reflected 

 from the chorion to the embryo, so that the tissue to be affected 

 is struck at the critical time in its development. It is incon- 

 ceivable that cyclopia should begin in an embryo after the eyes 

 are once started in normal development. Moreover, the same 

 is true regarding hare lip, for after the upper jaw has once been 

 well formed, the abnormality cannot develop. We may extend 

 this statement to include club-foot, spina bifida occulta, and 

 other types of malformation. In fact, in discussing the origin 

 of merosomatous monsters, hardly more has been stated by 

 most authors than that there has been an arrest of development, 

 but I have attempted to point out that the primary cause is in 

 the environment of the egg and that the arrested development 

 is associated with destruction of tissue. 



