166 



EXPERIMENTAL INOCULATIONS 



Preparation of sterile water. A number of test-tubes or small flasks of 50-100 c.c. 

 capacity should be three-quarters filled with water and sterilized at 115 C. When 

 wanted, aspirate the water out of the tubes or flasks with a Pasteur pipette. The 

 contents of any tube or flask opened and not used 'should be thrown away at once. 



Water may also be sterilized in larger quantities in flasks : but it is better to 

 use small vessels containing only sufficient water for one experiment. All risk of 

 contamination is then avoided. 



A number of sterile glass dishes, glass rods, platinum wires and Pasteur 

 pipettes must also be ready. 



Lastly, syringes and needles are necessary with which to inoculate the 

 virus into the tissues. 



(i) Inoculation syringes. 



There are numerous patterns of inoculation syringes, and this fact in itself 

 shows how difficult it is to obtain a syringe which fulfils all the conditions 

 required of it. A satisfactory syringe should 



1. Lend itself to sterilization in boiling water or in steam under pressure. 



2. Have perfectly water-tight joints and plunger, and be so constructed 

 as not to need frequent renewal of the parts. 



3. Be accurately graduated on the glass barrel or piston rod. 



Pasteur pipettes. A Pasteur pipette may on occasion be used as an inoculation 

 syringe. And for this purpose the drawn-out part is made short and slightly 

 curved, with a sharp point (fig. 133). [The opposite end is plugged 

 with wool and the pipette sterilized before use. A small bulb may 

 be very conveniently blown on the tube. ] The liquid to be inoculated 

 is sucked up into the pipette and the pointed end pushed through 

 the skin [or, when required, into the peritoneal cavity], and the 

 material deposited in the tissues by blowing through the plugged end. 

 This is all the apparatus that is necessary in a large number of cases. 



A. Older patterns. Of the older patterns of syringes the use 

 of which is now being given up, the following may be men- 

 tioned : 



Pravaz's syringe. One of the oldest and at the same time one of 

 the best from the point of view of the security of its joints is Pravaz's 

 syringe. But, unfortunately, the joints and the leather plunger will 

 not stand the temperature of boiling water. If it be used it must 

 be disinfected by soaking it in a 5 per cent, solution of carbolic acid 

 for several hours and subsequently rinsing well in sterile water. 



Syringes with air piston. Koch, Petri and others eliminated the 

 plunger. The glass cylinder forming the body of the syringe was fitted 

 at one end with a needle and at the other with an india-rubber ball : 

 FIG. 133. by squeezing the ball, the liquid was forced out. When used for 



Pasteur pipette injection however especially into tense tissues, the liquid either cannot 



modified for m- , J . 1,1 \ \ .1 -n -/i i mi. 



oculations. be inoculated or runs out when the needle is withdrawn. These syringes 



are not now in use. 



Straus' syringe. By substituting compressed elder pith for the leather in Pravaz's 

 plunger, Straus obtained a syringe which stands the temperature of boiling water and 

 of the autoclave very well. The plunger can be changed as often as is necessary, 

 but though it is easily done it takes some time ; moreover it has to be done fre- 

 quently since the elder pith rapidly loses its elasticity. With these reservations 

 the syringe is a good one. 



To renew the plunger. Take a piece of elder pith with a regular and fine grain, 

 cut off the outer, fibrous layer, and compress it between the fingers so as to flatten 

 it longitudinally as much as possible. Then cut out a small cylindrical piece to 

 fit the barrel of the syringe tightly. Perforate its centre with a needle heated to 

 redness in the flame and fix it on to the end of the piston rod. Then with a very 

 fine file polish its sides and introduce it into the barrel. By soaking in water for a 

 few minutes the elder pith swells and the plunger becomes water-tight. The 

 pith can also be compressed at will by means of the screw at the top of the piston rod. 



