SIO lloAKI* (»!■■ Ai.I.Mrrr.TUKE. 



rcssliil ill list". 'rii.it most ciiiployt'il in nicdiciiic is .•iiitist rcitttx-dcciis 

 sciuiii in tiic ircjilnifiit ol liluod-poisoiiiii;.'. 



'I'iif iiniimiiilv .Li.iiin'<l as tlic rcsiill ut nii ;iti;iii< nf ;i iliscnsc wiictlicr it 

 lie antitoxic, bactcryolitic or lioiji is a naturally a<<iuiif'l iniiaiinity. 



Ill tlu' cast' of liou cliolcia \vf tlo know thai a i-crtain aiiioiint of ini- 

 nniiiity is actiuiied. A lirood sow lliat lias siKt-ossfully withstood an 

 attark of discasi' has an cnhaiKMMl xaliio liccausp of the fact. The im- 

 UHinily whicli slir has aiqnircd is iiol lraiisiiii(t<'d lo licr offsprin.^. It is 

 an cxc('cdin.i,'ly d»'siial>lc (juality to lie ohtaiiicd in all, occui's in iialiirc 

 in so few. and at siuh ;zrcat itrice that ovoiy known artificial method has 

 ht'cn cmiiloycd to induce it. These will uow be consiihM'ed in some detail. 



Wictiuation.— Siiicf immunity i-esults from an attack of some diseases. 

 :iiid the immniiity gained fidiii a mild attack is jirolcclive the same as 

 for a severe attack, attempts liave liecn made to induce a mild form for 

 jirotection. Tills w.is tirst done in connection with smallpox. The pa- 

 tient dieted and put in as licalthy condition as possible and then the virus 

 was taken directly from a jiaticiit. care lieing- exercised to select one 

 suffering;' from a mild form. Tliis had the desired result in many cases 

 but often caused death. Mrus taken from a mild case might suddenly 

 acquire increased virulence witli fatal results. I-ater it was discovered 

 tliat jiatients vaccinated with cowpox in a natiu'al Avay in handlinc; 

 cattle were immune ti) smalliiox and tliat IIkisc sulferinjx from the cow- 

 ]iox iiad it in a very mild form couiiiared with those vaccinated with 

 smalljMix. This led to the 'abandoiimeiit of the human A'irus and the sub- 

 stitution of the bovine material or cowjiox. Seiisis and othei' serious 

 complications often resulted at first, but the methods of preparing the 

 virus, preserving, and using it, have been so greatly^ improved that it is 

 now used with a feeling of safety. AVo now know that the cowpox and 

 the smallpox are flie same diseases but the passage of the disease through 

 the cow reduces its virulence for the hiunan subject. Likewise, the im- 

 munity gained liy the bovine virus is not so strong or so enduring as that 

 from the liunmn. The operation of vaccination consists of abrading or 

 scratching tlie surface of the skin and rubtiing in the virus. Vaccination 

 has been tried for the prevention of hog cholera and SAvine plague but 

 without the degree of success that is essential in practice. 



Tlie virus taken from infected hogs is not satisfactory and there is 

 no otlier animal known to have the disease .so that it may be moditicnl 

 by i)assage through a different body. Attemiits to modify tlie virus by 

 artificial means has likewise been a failure. 



Inoculation. — Immunity may also be acquired by artificial means by 

 a method jiojiidarly known as inoculation. In this method the virulence 

 of the germs are reduced by artificial means. It has its best ai»plication in 

 the prevention of blackleg. The tissues of an animal having died of black- 

 leg are heated to such a degree as to nearly destroy all germs. A bit of 

 tissue is then rublied up Avitli some sterile water, filtered and injected into 



