290 A LETTER TO DR. HAYGARTH. 



animal, and the animal do well without it. I made the ex- 

 periment on a dog, and kept him a year and a half, without 

 observing his health the least impaired. From this, some have 

 concluded the spleen to be a useless weight, which is absurd, 

 when we consider that all animals with red blood have it. 

 Therefore it is more consistent with what we know of the animal 

 economy, to conclude that since an animal can do well without 

 it, there is probably some part of the body that can supply its 

 place. 



Insects have vesicles constructed in a similar way to ours, 

 but differing in colour. But insects have neither spleen, 

 thymus, nor lymphatic glands, and therefore in them probably 

 these vesicles are entirely fabricated in the lymphatic vessels. 

 But to us, and other of the more perfect animals, besides the 

 lymphatic vessels, nature has given those glands, that a proper 

 quantity of those important vesicles might be the better secured 

 to us, just as she has given us two ears, the better to secure 

 to us hearing through life, though we can hear perfectly well 

 with one. 



Thus, my dear friend, I have given you a sketch of my new 

 opinions. I rather expect from this merely to gratify your 

 longing than to convince you, for the subject is too intricate 

 to be communicated in a letter ; but I make no doubt of proving 

 these positions when I have leisure to handle the subject more 

 fully. Adieu ! Believe me ever sincerely your friend, 



WM. HEWSON. 



LONDON; July 19, 1773. 



