410 REPORT— 1869. 



senses direct to the organic nervous sj^mpathetic cbain. It may be in either 

 case an indirect impression convej'ed from within the body, and, as one -would 

 imagine by the blood, to that nervous chain. But why the nervous chain 

 shoukl thereupon lose its controlling power, what molecular change is com- 

 municated to it to make it lose its power, we cannot answer at present. We 

 must be content to wait, satisfied for the moment with the possession of a truth 

 which fifty years ago the most sanguine physiologist would not have dreamed 

 of, that there is a class of organic bodies by which we are able to induce, 

 in a simple physical way, what have been called up to this time emotional 

 phenomena. ' 



One other observation deserves a moment's expression, inasmuch as it 

 explains a well-known symptom which many persons have experienced. 

 If the heart be thrown into sudden action by any external cause, by breath- 

 ing, for example, the vapour of nitrite of amyl, there is produced in the head 

 a peculiar pulsating burring sound, which sometimes amounts to a whistle or 

 coo. In some forms of disease, especially in debility following upon emotional 

 distress or anxiety, this sound becomes persistent and intensely distressing. 

 In both cases the sound is produced by the same cause. The vascular ten- 

 sion reduced at those points of the body where the vessels pass through 

 rigid canals or openings, there is vibration set up in the resistant parts, 

 which vibration produces audible sound. In the entrance of the internal 

 carotid artery into the skuU by the carotid canal, we have a perfect arrange- 

 ment for the production of this pulsating murmur ; and as the canal is in close 

 and solid connexion with the organ of hearing, the murmur is clearly and 

 often painfully audible whenever the artery (if I may use the expression) is 

 not under guard, i. e. is not under the full control of the organic nervous 

 power, 



THE PHYSIOLOGICAL ACTION OF HYDRIDES. 



The first of the hydrides named in the Table, and the last, have been 

 studied in regard to their physiological action and values. 



Hydride of Methyl or Protylen. — This body, known commonly as fire- 

 damp in mines, and as marsh-gas on laud, is made by heating together 

 acetate of soda, caustic potassa, and well-dried lime. Its properties and 

 composition will be seen in the Table. I have already (at Dundee) reported 

 on the action of this hydride and have little to add to what was there 

 recorded. To make it produce rapid auicsthcsia the gas must be inhaled nearly 

 undiluted Math air. It produces no excitement, and recovery from its effects, 

 if the inhalation be stopped in time, is extremely rapid : a few seconds are, 

 indeed, sufficient to restore consciousness and muscular power. The gas can 

 only kill by a process of gradual negation of respii'ation, by replacing air re- 

 quired for the oxidation of the blood. It has no irritating properties, and is 

 breathed without causing spasm. I repeat here what I was able to state at 

 Dundee, that death from fire-damp must be of the easiest kind, must in fact 

 be as easy as going to sleep, a circumstance which accounts probably for the 

 sleep-like placidity and posture in which the dead have been found after fatal 

 accidents from inhaling this substance. From the circumstance that the hydride 

 is found in the air of marshes, it has been taxed as the cause of malarious fevers. 

 There is no evidence whatever to support this view — no evidence whatever 

 that the gas is anything more than an immediate and simply negative poison, 

 the effects of which cease so soon as the animal body has been removed from 

 its influence. It is certainly possible that a person exposed for several hours 

 to the gas mixed ^^•ith air would be reduced in power, and would suffer from 



