COMPARISON OF MY OBSERVATIONS WITH THOSE OF LEEUWENHOEK.
Although I made the preceding experiments with all the circumspection possible; and although I repeated them a number of times, I am persuaded that many things escaped my notice; I have only related what I saw, and what all the world may see, with a little art and much practice. In order to be free from prejudices, I endeavoured to forget what other naturalists asserted to have seen, conceiving that by so doing, I should be more certain of only seeing in fact what really appeared; and it was not till after I had digested my observations, that I compared them with those of Leeuwenhoek, &c. I by no means pretend to have greater abilities in microscopical observations than that great naturalist, who passed more than sixty years in making various experiments.
Notwithstanding the authority his observations may justly claim, it is surely permitted to examine and compare others with them. Truth can only be gained by such examinations, and errors discovered, particularly as we do it without any partiality, and in the sole view of establishing something fixed and certain on the nature of those moving bodies seen in the seminal liquors.
In November 1677, Leeuwenhoek, who had already communicated to the Royal Society of London many microscopical observations on the optic nerve, the blood, the juice of the plants, the texture of trees, rain-water, &c. addressed to Lord Brouncker, President of the Society, in the following words: "Postquam Exc.[S] &c. Dominus Professor Cranen me visitatione sua sæpius honorarat, litteris rogavis, Domino Ham concrato suo, quasdam observationum mearum, videndas darem. Hic dominus Ham me secundo invisens, secum in laguncula, vitrea semen viri, gonorrhæa laborantis, sponte destillatum, attulit, dicens, se post paucissimas temporis minutias (cum materia ilia jam in tantum esset resoluta ut fistulæ vitreæ immitti posset) animalcula viva in eo observasse, quæ caudam & ultra 24 horas non viventia judicabat; idem referebat se animalcula observasse mortua post sumptam ab ægroto therebintinam. Materiam prædicatam fistulæ vitreæ immissam, præsente Domino Ham, observavi, quasdamque in ea creaturas viventes, at post decursum 2 aut 3 horarum eamdem solus materiam observans, mortuas vidi.
[S] See Phil. Trans. No. 141, page 1041.
"Eamdem materiam (semen virile) non ægroti alicujus, non diuturna conservatione corruptam, vel post aliquot momenta fluidiorem factam, sed sani viri statim post ejectionem, ne interlabentibus quidem sex arteriæ pulsibus, sæpiuscule observavi, tantamque in ea viventium animalculorum multitudinem vidi, ut interdum plura quam 1000 in magnitudine arenæ sese moverent; non in toto semine, sed in materia fluida crassiori adhærente, ingentem illam animalculorum multitudinem observavi; in crassiori vero seminis materia quasi sine motu jacebant, quod inde provenire mihi imaginabar, quod materia illa crassa ex tam variis cohæreat partibus, ut animalcula in ea se movere nequirent; minora globulis sanguini ruborem adferentibus hæc animalcula erant, ut judicem, millena millia arenam grandiorem magnitudine non æquatura. Corpora corum rotunda, anteriora obtusa, posteriora ferme in aculeum desinentia habebant; cauda tenui longitudine corpus quinquies sexiesve excedente, & pellucida crassitiem vero ad 25 partem corporis habente prædita erant, adeo ut ea quoad figuram cum cyclaminis minoribus, longam caudam habentibus, optime, comparare queam; motu caudæ serpentino, aut ut anguillæ in aqua natantis progrediebantur; in materia vero aliquantulum crassiori caudam octies deciesve quidem evibrabant antequam latitudinem capilli procedebant. Interdum mihi imaginabar me internoscere posse adhuc varias in corpore horum animalculorum partes, quia vero continuo eas videre nequibam, de iis tacebo. His animalculis minora adhuc animalcula, quibus non nisi globuli figuram attribuere possum, permissa erant.
"Memini me ante tres aut quatuor annos, rogatu Domini Oldenburg, B. M. semen virile observasse, & prædicta animalia pro globulis habuisse; sed quia fastidiebam ab ulteriori inquisitione, & magis quidem a descriptione, tunc temporis eam omisi. Jam quoad partes ipsas, ex quibus crassam seminis materiam, quoad majorem sui partem consistere sæpius cum admiratione observavi, ea sunt tam varia ac multa vasa, imo in tanta multitudine hæc vasa vidi, ut credam me in unica seminis gutta plura observasse quam anatomico per integrum diem subjectum aliquod secanti occurrant. Quibus visis, firmiter credebam nulla in corpore humano jam formato esse vasa, quæ in semine virili bene constituto non reperiantur. Cum materia hæc per momenta quædam aëri fuisset exposita, prædicta vasorum multitudo in aquosam magnis oleaginosis globulis permistam materiam mutabatur, &c."