352 ANNUAL OF SCIENTIFIC DISCOVERY. 



rapidity of the propagation of the nervous agent in the spinal nerves," 

 M. Helmholtz describes at length some experiments of his, from which 

 he concludes that the nervous irritation passed over a space of 50 to 60 

 millimetres in from 0.0014 to 0.0020 of a second. The frogs experi- 

 mented on had been kept at a temperature of 2 to 6 Centigrade, 

 while that of the laboratory was 11 to 15. The lower the tempera- 

 ture, the less appears to be the rapidity of the nervous agent. 



DIRECT EXPLORATION OF THE INTERIOR OF THE EYE. 



DR. S. WOOD, of Cincinnati, has described a phenomena which sug- 

 gest a new 7 mode of direct exploration. He states that, by means of 

 a small double convex lens, of short focus, held near the eye, that 

 organ looking through it at a candle twelve or fifteen feet distant, 

 there will be perceived a large luminous disk, covered with dark and 

 light spots and dark streaks, which, after a momentary confusion, will 

 settle down into an unchanging picture ; which picture is composed 

 of the organs or internal parts of the eye. The eye is thus enabled to 

 view its own internal organization, to have a beautiful exhibition of 

 the vessels of the cornea, of the distribution of the lachrymal secre- 

 tions in the act of winking, and to see into the nature and cause of 

 musca volitantes. Western Lancet, Nov., 1849. 



ANIMAL HEAT. 



M. MAGENDIE, in his lectures at the College of France, has detailed 

 some experiments upon the effects of extremes of temperature upon 

 animals. The object in view was the solution of the questions, 

 Whether animals really possess the power of preserving their temper- 

 ature, whatever may bs that of the medium surrounding them? 

 What are the limits of the temperatures they can support ? What are 

 the phenomena which accompany death caused by extremes of tem- 

 perature? Rabbits, dogs, and guinea-pigs were employed, and the 

 temperature ascertained by a thermometer introduced into the rectum. 

 Effects of high temperature : Death occurred the more rapidly, cceteris 

 paribus, the higher the temperature employed. Thus, of five rabbits, 

 the first exposed to 248 F. died in 7 minutes, and the last, exposed 

 to 140 3 , in 33 minutes. Three dogs, exposed respectively to 212, 

 194, and 176 3 , died in 18, 24, and 30 minutes. The same rule ap- 

 plies to birds, but they bear high temperature for a shorter period than 

 mammals. Cold-blooded animals endure it longer. Rabbits exposed 

 from 140 to 212 lost in weight about 15 grains per minute. The 

 loss was not so much in proportion to the degree of elevation of tem- 

 perature, as to the duration of a high one ; and it is dependent more 

 upon pulmonary transpiration than cutaneous. Thus a rabbit placed 

 in the heated stove with its head out lost only 10 grammes, while one 

 with its head within and its body out, lost 25 grammes. A living 

 rabbit, having a temperature of 102, and one just killed with a tem- 

 perature of 87, were placed in the stove at 176. After 20 minutes, 

 the former died convulsed, having acquired a temperature of 112 in 



