336 
Dr Nuttall, Further Observations on Blood. 
tions of Alligator sinensis and Testudo ibera, a faint clouding with 
A. mississippiensis and Chelone midas. This anti-serum produced 
no clouding in mammalian or other bloods. Should further in- 
vestigations show similar reactions with other reptilian bloods, 
then we may perhaps be able to assume that the egg still possesses 
a vestige of reptilian character. It is however too early to draw 
any conclusions. 
Anti-alligator serum, prepared by injecting rabbits with the 
serum of A. mississippiensis, produced a reaction on being added 
to serum dilutions from A. mississippiensis and A. sinensis, a faint 
clouding in the blood of Chelone midas. 
Anti-turtle serum (from Chelone midas) acted upon turtle blood, 
but in addition produced a marked clouding in the blood of Testudo 
ibera, a very faint clouding with A. mississippiensis, no other bloods 
being affected. 
Anti-lobster serum (from Homarus vulgaris) reacted with 
lobster serum dilutions, produced marked clouding with blood 
of Astacus fluviatilis, but exerted no effect whatever on any of the 
250 bloods examined, as in the preceding cases 1 . 
I come finally to the consideration of the reaction which takes 
place in non-homologous or distantly related bloods when these 
are allowed to stand. From the first, I found it necessary, in 
making these tests, to put a time limit upon them. This may 
appear to be a rather arbitrary proceeding. My time limit has 
usually been five minutes at average temperatures in the laboratory. 
A powerful anti-serum will certainly have acted within that time 
upon its homologous blood-dilution ; with powerful fresh anti-sera 
the reaction takes place almost instantaneously. On the other 
hand, if we allow the mixtures of anti-sera and bloods to stand, 
a reaction takes place slowly with non-homologous bloods. The 
results I have hitherto obtained tend however to prove that anti- 
mammalian sera only produce these later reactions in mammalian 
bloods, and anti-avian sera act similarly on avian sera alone. 
I am at present engaged in carefully observing these slower 
reactions. The results above recorded are based upon observations 
made within the arbitrary time limit. 
1 Note whilst going through the press : — I have since found that anti-lobster 
serum produced slight reactions or marked clouding with blood dilutions of five 
species of crab, viz. Portunus depurator, P.puber, Carcinus maenas, Cancer pa gurus, 
Eupagurvs bernhardus. 
