THREATENED WITH BLINDNESS. 219 



and for some months he was obliged to abate 

 his activity, and to refrain even from writing 

 a letter. During this time, while he was shut 

 up in a darkened room, he practiced the study 

 of fossils by touch alone, using even the tip 

 of the tongue to feel out the impression, wher 

 the fingers were not sufficiently sensitive. He 

 said he was sure at the time that he could 

 bring himself in this way to such delicacy of 

 touch that the loss of sight would not oblige 

 him to abandon his work. After some months 

 his eyes improved, and though at times threat- 

 ened with a return of the same malady, he 

 was able, throughout life, to use his eyes more 

 uninterruptedly than most persons. His lec- 

 tures, always delivered extemporaneously, do 

 not seem to have been suspended for any 

 length of time. 



The following letter from Agassiz to Hum- 

 )ldt is taken from a rough and incomplete 

 draught, which was evidently put aside (per- 

 haps on account of the trouble in his eyes), 

 and only completed in the following May. 

 Although imperfect, it explains Humboldt's 

 answer, which is not only interesting in itself, 

 but throws light on Agassiz's work at this 

 period. 



