1 30 Dr. Hodgkin and J.J. Lister's Microscopical Observations 



water, even while the head is i^ept up it is as speedily drowned 

 as a cormorant under it. For this tact we can give no other 

 adequate solution, than by referring it to some peculiarity of 

 the nervous system. It may indeed be argued, that the cause 

 of death in this instance results proximately from the spas- 

 modic closure of the glottis, produced by the shock of immer- 

 sion. But why should this occur in the land-bird more than in 

 the cormorant? 



Not only is the quality but also the qiiantitij of blood in 

 aquatic animals different from that in land-animals. In the 

 former, the quantity is much greater in proportion to their size. 

 In whales and seals for instance, it is excessive ; and their ca- 

 pacity of great and continued muscular exertion is also stri- 

 kingly conspicuous. Can this depend chiefly on the different 

 quality or increased quantity of ihe vital fluid ; or on some 

 particular condition of the nervous energy ? 



On a review of what I have here advanced on this subject, 

 it appears to me that we may be justified in assuming, that 

 the nervous system of aquatic animals breathing through lungs 

 is so constituted, that the venous blood requires a much 

 longer period to circulate in the brain before it produces 

 death than in land-animals. That the natural and healthy 

 state of their blood is subartcrial ; and that it is not necessary, 

 in accounting for the superior power which they possess of 

 suspending respiration, to presume any peculiarity of organi- 

 zation. 



These views I have long entertained ; and they are founded 



on an ample experience of many years, both as a zoologist and 



a sportsman, in situations peculiarly favourable for accurate 



observation on the oeconomy and structure of aquatic animals. 



Balta Sound, Zetland, April 1827. 



XXVI. Notice of some Miscroscopic Obse^-vations of the 

 Blood and Animal Tissues. By Dr. Hodgkin and J. J. 

 Lister.* 



T^HE powerful compound achromatic microscope in the 

 -*- possession of J. J. Lister, being, as I have reason to think, 

 far superior to any thing of the kind yet produced in this 

 country, a short account of its application to animal struc- 

 tures will probably be considered not altogether uninterest- 

 ing. This microscope is the only one, which, up to the present 

 time, has borne a comparison with the justly celebrated instru- 

 ments of Amici. After repeated comparative trials, with the 



• Communicated In Dr. Hodgkin, 



most 



