The progeny of meat-fed rats are usually poorly developed, and show a high mortality in early life. Some statistics on this point are given. Of ninety-three rats born of meat-fed parents (ox-flesh and horse-flesh), nineteen (20 per cent.) were alive at the end of two months ; while of ninety-seven rats born of bread-and-milk-fed rats, eiyhty-two (84 per cent.) were then alive and in apparent health. The state of development of the progeny of bread-and-milk-fed rats (Fig. 9a) in comparison with that of meat-fed subjects (Fig. 9b) is illustrated in Fig. 9, p. 566, for animals six weeks old. The meat-fed animal (Fig. 9d) was puny and ill-developed, with scanty hair and dry skin, a picture of general marasmus. It died two weeks after the photograph was taken. One of the thirteen meat-fed litters (an ox-flesh litter) was a striking exception to the general rule. When two months old this litter, nine in number, appeared to be in perfect health, their average weight and general appearance being quite up to the normal standard. The high mortality in early life of the second generation of meat-fed rats is probably due in great part to the defective power of lactation in the mothers.
Chart 5. The influence of a horse-flesh diet on adult rats. The dark line represents the average weight of nine adult rats fed fur live months on a horse-flesh diet. The arrows indicate deaths.
Some observations were made on the recuperative power of a normal diet in animals which had deteriorated in consequence of having been fed for some time on an abnormal dietary. The results in the case of flesh-fed animals were in this instance controlled by comparison with those obtained from animals fed on (a) an exclusively rice diet, and (b) an exclusively porridge (made with milk) diet. Observations were made on animals of both the first and second generation.
After the primary observation on each diet had been in progress for five weeks and the natural course of events in each group had been determined, an average representative of the rice-fed, flesh-fed, and porridge-fed animals was taken and put on a diet of bread and sweet milk, the amount of each being unrestricted. This done on 4th June. At this time the animals showed marked evidence of retarded growth and a considerable degree of respiratory embarrassment The change of diet was immediately followed by a marked increase in the rate of growth, this being pronounced in all three cases (see Chart 6). The improvement in the general condition of the animals was associated with an improvement in the respirations, which became less frequent, less noisy, and with fewer accompaniments. The subject which was originally fed on rice died after five weeks of the new diet ; the other two were alive and in fair health in the middle of October. It has to be noted, however, that their average weight in October was 136 grammes, considerably less than the average of a healthy bread-and-milk-fed subject of the same age. The results of this observation showed that the change of diet to bread and sweet milk in all three subjects was followed by a rapid and marked improvement in the general condition and also by a marked improvement in respiration. The recovery from the respiratory embarrassment was, however, not complete. It also showed that the growth of the animals had been permanently stunted by the use of the abnormal diet in early life.
Chart 6. The effects of a bread and need milk diet on young rats previously fed on an abnormal dietary. The corral represent the weights of three young rats that were fed on porridge, rice, and horse-flesh respectively fur live weeks, and were then transferred on the thirty-eighth day to a bread and sweet milk diet.
With the object of testing the immediate results observed to follow the change of diet, another animal was taken from each group and was fed on the control diet of bread and skimmed milk. Chart 7 shows the record of weight of these animals for the period of six weeks, during which they were fed on rice, porridge, and horse-flesh diet respectively, and thereafter on the control diet. The condition of the rice-fed subject when removed was such that our experience led us to believe that it could not live more than, at the outside, one or two days longer on that diet. After the change of diet there was a rapid and immediate improvement in the condition of all three animals. The result was even more striking than in the case of the three animals the diet of which had been changed to bread and sweet milk (see chart). All three animals were alive and in fair condition in the middle of October, their average weight at that time (138 grammes) being, however, below the normal.