36 
Transactions Texas Academy of Science. — 1907. 
blood, which constitute the substrate vulnerable to the species of bac- 
terium, were either destroyed or the atomic structure was changed in 
such manner that the specific vulnerability to the bacteria was lost. 
Under these conditions no infection can follow the introduction of the 
bacteria ; there can be no development of toxins or toxalbumins, and the 
phagocytes will, therefore, destroy the bacteria as they do other innoc- 
uous, positive chemotactic substances. In the second instance, both 
conditions necessary to pathogenesis are present (the infectious bacteria 
and a vulnerable substrate), infection will, therefore, occur with a de- 
velopment of toxin or toxalbumins, and the phagocytes will be driven 
from the field by the bacteria poisons, and may be destroyed by the 
same agents. 
OPSONINS. 
A new and fascinating treatment of infectious diseases has recently 
come into vogue and seems to be rapidly gaining in popularity. This 
treatment is based upon a specific pow'er in making pathogenic bacteria 
susceptible to phagocytic destruction, that opsonin is said to possess. 
Only a few years ago we were taught by Metschnikoff and his school 
that the phagocytes of our serum were the sole defenders of our bodies 
from infection by invading pathogenic bacteria. More recently, under 
the teaching of Wright and Douglass, we are led to believe that the 
phagocytes alone can not accomplish this work, but must be assisted 
by opsonin. It is claimed that opsonin first weakens the resisting power 
of the bacteria, and not until then can phagocytes take the bacteria in 
and destroy them — that neither opsonin alone nor phagocytes alone is 
able to destroy the bacteria, but when both are present their combined 
action not only kills the bacteria but causes them to be taken in and 
digested by the phagocytes. This claim is based upon the fact that 
serum assumed to contain opsonin loses its bactericidal power when it 
is heated to 55° C., but the lost function is restored by the addition of 
a little fresh serum ; the serum that is added need not be native serum, 
since serum from alien species will do as well. The opsonists say that 
heating the serum destroyed its opsonin and the phagocytic power of 
the leucocytes, and that the restoration of these functions by the addi- 
tion of fresh serum is due to the opsonin the serum contained. We 
may, at least, learn from these phenomena, since the addition of alien 
serum will restore bactericidal power to overheated serum, that neither 
the serum nor its opsonin are specific in their action. 
The opsonic explanation of the phenomena named, beautiful and at- 
tractive as it appears, is not the only one, nor, as I view it, the one in 
harmony with known physiological functions, that is capable of inter- 
preting the facts upon which the opsonic theory is based. I will try to 
