140 THE AMERICAN NATURALIST [Vol. LIV 



fected animals which are fairly able to walk may not fall 

 over even as a result of an auditory stimulus. They give 

 a jump, much more pronounced than the start of normal 

 individuals, but manage to stay on their feet. Further- 

 more, even the more affected ones become less sensitive 

 to repeated stimulation, and may after several reactions 

 fail to respond sufficiently to make them lose their balance. 



In the more severe stages the reaction appears to simu- 

 late intentional tremor, in that it follows attempts at vol- 

 untary movements of the hind legs. In less severe cases 

 the animal can use the legs if free from other nervous 

 excitation. It would appear therefore that the condition 

 is induced by sudden nervous excitement, the degree of 

 the stimulus necessary to cause complete lack of mus- 

 cular control depending on the stage of progress of the 

 affection. 



The severe spasms commonly last but a few moments. 

 If a guinea-pig stiffened out in one of the spasms is taken 

 in the hand it can soon be felt to relax, following which 

 it either lies quiet or makes slow movements of the head 

 and to some extent of the legs as previously described. 



Etiology 



A number of possibilities suggest themselves as causes 

 of the disease described in this paper, and these will be 

 discussed in order. 



1. As mentioned in the following section, digestive dis- 

 turbances may cause in sheep a condition very similar in 

 many of its symptoms to the spasm of our guinea-pigs. 

 Is it not possible that these were originally induced by 

 some similar cause? It is true that at times, especially 

 in the early part of the work, we have had some trouble 

 from improper feeding, notably when we attempted to 

 substitute sugar beets for carrots and cabbage. "While, 

 however, inadequate diet may cause scurvy and other 

 effects, we have no reason to believe that it ever produces 

 a condition which could be mistaken for the congenital 

 palsy. Furthermore, palsy never occurs in the descend- 



