Memoirs of Erasj^us Darwin, M.JJ. 333 



of vision of this eye to a similar-degree of imperfection with 

 the other, should be worn some hours every day. Or the 

 better eye should be totally darkened by a tin cup covered 

 with black silk for some hours daily, by which means the 

 better eye will be gradually weakened by the want of use, • 

 and the worse eye will he gradually strengthened by using it. 

 Covering an inflamed eve in children for weeks together, is 



CD O ^ 



very liable to produce squinting, for the same reason. 



Asthma humorale. — The humoral asthma probably con- 

 sists in a temporary anasarca of the lungs, which may be 

 owing to a temporary defect of lymphatic absorption. Its 

 cause is nevertheless at present very ohscure, since a tem- 

 porary deficiency of venous absorption, at the extremities of 

 the pulmonary or bronchial veins, might occasion a similar 

 difficulty of respiration. Or it might be supposed, that the 

 lymph effused into the cavity of the chest might, by some 

 additional heat during sleep, acquire an aerial form, and 

 thus compress the lungs; and on this circumstance the re- 

 lief, which these patients receive from cold air, would be 

 readily accounted for. 



The paroxysms attack the patient in his first sleep, when 

 the circulation through the lungs in weak people wants the 

 assistance of the voluntary power. And hence the absorb- 

 ents of the lungs are less able to fulfil the whole of their 

 duty. And part of the thin mucus, which is secreted into 

 the air-cells, remains there unabsorbed, and occasions the 

 difficult respiration, which awakes the patient. And the 

 violent exertions of the muscles of respiration, which suc- 

 ceed, are excited by the pain of suffocation, for the purpose 

 of pushing forwards the blood through the compressed ca^ 

 pillaries, and to promote the absorption of the effused lymph. 



In-this the humoral differs from the convulsive asthma, 

 as in that there is probably no accumulated fluid to be ab~ 

 sorbed ; and the violent respiration is only an exertion for 

 the purpose of relieving pain, either in the lungs or in some 

 distant part, as in other convulsions, or epilepsy; and in 

 this respect the fits of humoral and convulsive asthma essen- 

 tially differ from each other, contrary to the opinion ex- 

 pressed without sufficient considcratign. 



The 



