4 "CM. JACKSON 



system), although data are wanting to determine this point. The 

 external characters whereby the sexes may be distinguished in 

 young rats have been described by Jackson ('12). 



In general, the albino rat remains healthy and thrives in cap- 

 tivity. The chief exception noted is the frequent tendency to 

 lung disease, especially in the older rats and more rarely in the 

 younger. Two forms of disease were observed. The first is an 

 acute pneumonitis, which is usually fatal. This form appeared 

 but once in a period of three years. It occurred as an epidemic 

 which in a short time destroyed nearly the entire colony. This 

 epidemic was caused by a specific bacterium, bacillus muris, as 

 determined by Mitchell ('12). The second form of lung disease 

 noted is a chronic disturbance which is common in the wild 

 Norway rat at Columbia as well as in the domesticated albino. 

 It appears to develop first in the form of multiple small clear 

 spots scattered over the surface of the lung. Later these spots 

 may form small abscesses, or lead to the consolidation of one or 

 more lobes. An associated catarrhal condition of the respiratory 

 mucosa causes an audible snuffling or wheezing, through which 

 the disease may usually be recognized when well developed. It 

 usually is not fatal, or at least not immediately so, and in some 

 cases does not appreciably affect the growth or the general state 

 of nutrition. Generally, however, it tends to produce more or 

 less emaciation. This is probably the same disease as the pneu- 

 monia mentioned by King ('11) and by Currie ('10). Mitchell 

 ('12) failed in repeated attempts to find in this disease the spe- 

 cific bacterium causing the first form, and its etiology appears 

 uncertain. 



Animals affected with lung disease were excluded from the 

 present data except in some cases in which the lesions were slight 

 and it appeared necessary to exclude only the lungs. This was 

 the case in 3 of the 43 albino rats dissected at the age of ten 

 weeks, 11 of 41 at five months, and 20 of 25 at one year. Even 

 though the lesions were slight, however, it is probable that the 

 average body weight at five months, and especially at one year, 

 is somewhat below the normal. » 



