26 SIZE INHERITANCE IN RABBITS. 



through the year. On account of a lack of room, guinea pigs were 

 kept in the same pens with the rabbits that were not being bred. The 

 normal pen held one rabbit and six pigs. This arrangement seemed 

 to work very successfully. Certain rabbits would not live peaceably 

 with certain pigs, but in such cases suitable changes were always made. 

 Some growth curves show temporary losses due to hostile relations 

 with pigs, but these cases are not numerous and complete recovery is 

 found in every case. 



While the health of the animals in general was very good, a disease 

 known as "snuffles" was common. The symptoms of this are an 

 apparent cold in the head and in many cases a sudden loss in weight, 

 although many rabbits that showed the first symptom failed to lose 

 weight. A study of the growth curves shows (see p. 43) that such 

 abrupt losses were made up in the course of a few months. The pres- 

 ence of "snuffles" alone, then, did not seem cause for discarding an 

 animal. When there was doubt as to the recovery of an animal, this 

 one was not used. But such cases were very infrequent. In man most 

 illnesses affect the body weight, but seldom is the ultimate weight or size 

 changed thereby. The loss from sickness has been large. There have 

 been recorded 364 individuals in back crosses to c?2319. Of these 240 

 have been used. Besides such losses many animals not recorded died 

 of infantile diarrhoea and coccidiosis, while numerous litters from first 

 matings of Fi animals were eaten by the mother. 



The growth curves give ample evidence that each animal seemingly 

 attempts to attain a certain weight; that, for losses due to any cause, 

 there are subsequent compensating increases in the rates of growth, 

 unless the animal does not recover. Minot (1891) arrived at a similar 

 conclusion in his study of the growth of guinea pigs and he cites the 

 case of childhood disease in relation to mature size. That the bones 

 do not show such marked interruptions and variations in growth as 

 the body weight is very apparent. Donaldson (1911) speaks of this 

 as common observation. Careful studies of the growth of bones under 

 favorable and adverse conditions have been carried on by Waters (1908). 

 In cattle the height at the withers increases while the body weight is 

 kept constant. This is even true for animals whose body weight is 

 made to decrease. Curves of the increase in height of animals con- 

 stantly gaining in body weight, of animals maintained at the same 

 weight, and of animals constantly losing weight were parallel for four 

 months. Then the rate of the increase in height of the animal losing 

 weight began to fall off; this was followed in a month by the flattening 

 of the curve of the animal maintained at a constant weight. In the 

 light of these results it seems fair to believe that in the case of animals 

 that have lost weight from any cause and made it up, the lengths of 

 the bones have not been permanently altered. 



