On the Transmission of Cow-pock Matter to America. 277 



nerve, necessary for the production of a membrane so very thin 

 and delicate as the retina appears to be in its texture. Some 

 proportion certainly is discoveral)le between the sclerotic coat 

 and the dura mater, and also between the pia mater and the 

 choroid membrane ; — but can any necessary correspondence be 

 discovered between the volume of matter contained in the trunk 

 of the optic nerve, and the small quantity requisite to form that 

 thin lining for the choroides, called the retina ? 



In the last place, no useful purpose has ever vet been assigned, 

 nor can possibly be conceived to arise from leaving a spot equal 

 to the base of the nerve destitute of the choroides, and totally 

 insensible to the rays of light. Besides, to impute either a total 

 or partial insensibility to any disposition of a substance which 

 is allowed by every physiologist to be the grand medium in 

 the animal oeconomy, through which impressions on the organs 

 of sense are communicated to the common sensory, is, to say the 

 l)est of it, an unaccountable anomaly in the nervous system. 

 I am, sir. 



Your obedient servant, 



Wycombe, .April J, 1817. ANDREW HoRN. 



LXIX. On the Priority of the Transmi'ision of Cow-pock Mat- 

 ter to America. By T. J. Pettigrew, Esq. 



To Mr. Tillock. 



Sir, — XN the last Number of your Magazine, a correspondent 

 under the signature of " Play-Fair" expresses his surprise to 

 find it stated in my Memoirs of the Life and Writings of the late 

 Dr. Lettsom, that the vaccine lymph was first sent across the 

 Atlantic by Dr. L., and consigned to the care of his friend Dr. 

 Waterhouse of Cambridge, Massachusetts, from whence it spread 

 through the United States. This is said to be untrue ; That 

 " vaccine lymph had been jjreviously sent by Dr. Geo. Pearson 

 to Dr. Chichester, now a resident physician at Bath, l)ut at that 

 time in very extensive practice at Charleston in South Carolina." 

 Reference is also given to the Philosophical Magazine, vol. xvi. 

 p. 252, for the particulars of the vaccination of one individual in 

 the winter of 1799 by Dr. C. 



Nothing can be further from my wish than to attribute that 

 to any individual which does not appear to be jusUv his due ; 

 and had I not been informed by the highest authority on this 

 subject, that Dr. Lettsom had been the first to transmit to 

 America this inestimable treasure, I certainly should not have 

 ventured to state it in my publication. The notice of your cor- 

 S '<i respondent 



