STRUCTURE AND DEVELOPMENTAL RATE 245 



the studies by Mall ('17) and many others that localized anom- 

 alies are quite frequent in both normal and pathological human 

 specimens. The localized anomaly may involve only the eye, 

 only the bilaterality of the brain, only the ear, only the mouth 

 structures, only the kidneys (I have dissected two fetuses at 

 term neither of which possessed any evidence of a kidney, but 

 one of which was otherwise structurally normal), only the geni- 

 talia, etc. It is evident that such anomalies could not occur 

 unless there was a certain moment of specific and peculiar sus- 

 ceptibility on the part of each organ during which any unfavor- 

 able condition would act on it in a selective way. Of course, the 

 specific action of certain substances on certain embryonic buds 

 would give a possible explanation, but there is so much strong 

 positive evidence in the present study as well as from other sources 

 against this once attractive possibility that it can well be dis- 

 carded. A strong point of evidence is the fact that a typical 

 defect of one organ can be induced by a great number of treat- 

 ments, and different defects of many different organs can all be 

 induced by one and the same treatment. In every case the result 

 depends upon the developmental time during which the treatment 

 acts and not upon chemical or physical properties of the sub- 

 stance used. As repeatedly shown, the primary effect in all in- 

 stances is simply a slowing in the rate of development. 



c. Developmental rate and postnatal changes 



The relations between the rate of growth and particular de- 

 velopmental moments found in the embryo probably continue to 

 be of importance during postnatal development as well. The 

 numerous studies on inanition in rats and other mammals bear 

 on the same general problem as that considered in the present 

 report. The one important effect that inanition might have on 

 the subsequent history of a developing individual would be the 

 malformation and arrest in development of certain tissues or 

 parts. After birth a number of important organs and tissues 

 still have a considerable degree of growth and differentiation to 

 accomplish, and very probably the same rules apply to this activ- 



