CHAP. II.] THE BLOOD. 25 



serted into the artery and vein of the animals to be experimented upon ', 

 which should be deeply anaesthetized 2 * The clips which control the entrance 

 of blood from the cardiac side of the arterial and the distal side of the venous 

 cannula having been removed or opened, blood is allowed completely to fill 

 the elastic tubes attached to the cannulae, which are held at a fairly high 

 level so as to allow the blood to rise and expel the air before it. The 

 instant the tubes are filled their open ends are slipped over the ends 

 of A and B. 



The reservoir R having been placed in its lower position, the stop-cocks 

 of A and B are opened ; blood will then flow from the artery and vein into 

 the respective tubes. As soon as enough has been obtained the stop-cocks 

 are closed, and the tubes are simultaneously shaken by assistants so 

 as to defibrinate their contents. On placing the two tubes side by side 

 the contrast between the colour of arterial and venous blood will appear 

 most striking. 



A detailed description of this procedure has been given as, mutatis 

 mutandis, it illustrates the method in which blood can be obtained from 

 blood-vessels without being brought in contact with air, not only for 

 purposes of class demonstration, but also in researches on the gases of the 

 blood.. 



Where it is required to keep the blood for some hours, as for example 

 in order to make repeated analyses, one or both tubes may be taken out of 

 their respective clamps and laid in troughs containing broken ice. In some 

 cases it is desirable to obtain two separate samples of the same blood ; in 

 such cases the free upper ends of A and B have attached to them a T tube, 

 to which is connected the elastic tube leading to the artery or vein. The 

 blood-stream will then divide itself equally between the two "tubes. 



Although to the naked eye the blood appears to be a homo- 

 geneous red liquid, it is found on microscopic examination to 

 consist of a colourless fluid the so-called liquor sanguinis, or 

 plasma of the blood holding in suspension large numbers of solid 

 bodies, the coloured and colourless corpuscles of the blood. It is 

 the former of these which preponderate very greatly over the latter, 

 and which by the colouring matter, haemoglobin, of which tbey 

 mainly consist, confer upon the blood its red colour ; the shade 

 of this at any time depends, as will be shewn in the sequel, chiefly 



1 Handbook for Physiological Laboratory, p. 212. 



2 The Author would very strongly recommend all experimenters who have occasion 

 to perform experiments upon the lower animals, and especially dogs, to employ as 

 the chief means of producing insensibility to pain, subcutaneous injections of morphia. 

 Solutions of bimeconate of morphia may be obtained which contain as much as 

 two grains in half a drachm. As large a dose as two grains of the bimecoiiate 

 may with perfect safety be injected under the skin of a dog of medium size; the 

 injection is followed in about half an hour by salivation and by a staggering gait, and 

 then by deep somnolence. In this state the animal is quite passive, and may without 

 a struggle and without any fear being evinced on its part, be properly fixed, and then 

 rendered completely insensitive to pain by the administration of ether or chloroform ; 

 as was pointed out by Claude Bernard, under these circumstances chloroform anaesthesia 

 is induced with remarkable ease, and persists for a long time. This method not only 

 abolishes the fear which often must constitute the most important part of the pain in- 

 flicted by a physiological experiment, but in those rare cases where the animal must be 

 allowed to recover after the experimental proceeding has been carried out, the long period 

 of narcotism which succeeds it secures the absolute and beneficial rest of the animal. 



