Erysipelas and many other streptococcic infections appear as primary toxic diseases with a short incubation. Active immune sera in sufficient amounts injected in time give good results. Often a marked change in the symptoms is seen toward the 8th day, a fact which could be considered to indicate passage into the allergic phase. Many other manifestations of streptococcal infections, such as those seen in rheumatic fever, can be considered allergic.

The glomerulonephritis which appears as a complication of scarlet fever or of pharyngeal streptococcic infection is especially interesting. While a change in general symptoms in these infections is seen toward the 8th day, this complication usually appears toward the 24th day. The intervention of a secondary antigen resulting from the bond between lipids and the renal tissues can be hypothecated in the light of studies concerning immunological defense processes against tissues, which we present in the following pages.

We do not want to leave the problem of infectious diseases without a few more words about the use of lipids in the defense mechanism against microbes. The fact that lipids liberated in the first defense responses are bound to microbes and intervene in this complex form to promote the appearance of higher defense processes has led us to use similar bonds in order to stimulate this defense. We have seen above how lipids other than those offered by the infected organism can be used. The injection of killed microbes treated with lipoacid from heterogeneous sources, such as from species naturally refractory to the microbe, has enhanced the defense mechanism. Microbes treated with lipoacids of the tubercle bacilli or of Bixa orellana were seen to induce a strong specific allergic response.

Interesting results were obtained through the use of insaponifiable fractions bound to the microbes. The fractions obtained from refractory species appeared to be most effective in enhancing the defense mechanism in general. The insaponifiable fractions obtained from the entire body of rats, animals refractory to most infections, gave the best results for most of the infections studied.

In these investigations, in addition to using killed microbes treated with lipids in vitro, we employed another method to treat the microbes. Lipoids were added to the media in which the organisms were grown. Some of the lipoids were seen to increase, and others to decrease, microbial virulence. Killed and used as vaccines in cases of resistant infections, these lipoid treated microbes were seen to induce more effective immunization.

Experiments in progress indicate the possibility of using such microbes —and even viruses so treated—to obtain long lasting immunity. Microbes with very reduced virulence are used as live vaccines. Their capacity to induce effective defense responses in a short time also has led to their use as "late" vaccines, i.e., vaccines which can be administered during the incubation time of an infection. As these studies are still in progress an evaluation of the results is not yet possible.

An interesting aspect of the influence exerted by lipids upon microorganisms is their use in producing qualitative changes in antibiotics. Preliminary research shows that the addition of lipids of the microbes against which more active antibiotics are sought seems to alter the antibiotics so that they have a higher degree of specificity against these microbes.