162 PHYSIOLOGY 



smallest post-operative mortality when carefully tamed and 

 gentle rats were used. The effects observed were all measured 

 in relation to litter mate controls of the respective test animals. 



Effect on body length, body weight and tail length (Hammett, 

 '23 and '24), "Thypars." The growth of the body in weight 

 was the most retarded. The retardation was more marked in the 

 females. A lesser retardation of gross growth occurred when the 

 thyroid apparatus was removed at 75 days. 



"Parathys." The same effects were observed, but to a lesser 

 degree, in the rats operated at 100 days. In those from which the 

 parathyroids were removed at 75 days the gross growth of the 

 males was more retarded than was that of the females. Table 117. 



Effects on growth and composition of the long bones (Hammett, 

 '23, '24). In the "Thypars" there is retardation of growth of 

 humerus and femur in length and weight. Ossification is retarded 

 and dessication is produced. The humerus is more affected than 

 the femur. The calcium of the ash is not affected in the males but 

 is decreased in the females. In both sexes the magnesium and 

 phosphorus tend to be increased. 



In the "Parathys" there is retardation of growth in length and 

 weight of the long bones, but to a lesser degree than in the 

 "Thypars." No disturbance in the percentage of ash, water or 

 organic matter is caused in the males. In the females ossification 

 is retarded. In the males there is no change in calcium content 

 of the ash, but the magnesium and phosphorus increase. In 

 the females the latter occurs, together with a decrease in calcium. 



Effect on the incisor teeth (Hammett, '22). "Thypars." Defects 

 of the incisor teeth do not usually occur. 



"Parathys." (Operation at 75 days). Fragility, leading to 

 the breaking off of the tooth; a change from the normal semi- 

 translucency to a pathological snowy white opacity, together 

 with a tendency to loss of pigment and to overgrowth due to 

 displacement, all occur frequently. 



These effects, not found in the "Thypars," from which the 

 parathyroids were also removed, are interpreted as "expression 

 of a summation of stimulation of metabolism." 



