The Physician says: "Observe the miniature hounds that swimmeth in they father's urine!
He hath been stricken by the rabies!"
The Boy says: "Bust Master Arnau... My father hath swapped his urine for the cow's."
The Physician Says: Then your cow doth have the rabies, as testified by presence of the hounds!"
Here we have a typical medieval scene in which a doctor holds a matula full of urine up to the light in order to diagnose his patient. However the producer of this urine is nowhere in sight. The physician has been sent urine by proxy.
Many physicians such as Arnau of Villanova, pictured here, typically liked to see their patient face to face. However many doctors in the Middle Ages felt that they could do just as good a job at diagnosis and treatment of their patients with a urine sample alone. Here a young man has brought his father's urine to the doctor for analysis.
Medieval medical visual inspection of night water included the note of color, residue, clarity, bubbles, floating bodies, and in Arnau's case the presence of teensy tiny dogs suspended in the micturate of rabid patients. Physicians also used smell and taste (Ick!) to help diagnose illness. Apparently there are a number of pathologies of protein metabolism, hormonal secretion, etc. that can be determined through simply looking, sniffing, and tasting (Ick!) someone's pee.
So what's with the reference to the cow? Apparently people used to replace their urine with the urine of a friend or animal, or use white wine (makes tasting easier!) to fool the doctor. Although present day urine switches usually are motivated by employers looking for drugs in the urine of their workers, I think it's easy for us to understand the motivation of someone wanting to avoid a dire diagnosis, or just wanting to play a trick on the doctor.
Why a cow? As reference to a centuries olde story (so olde it has an "e" on the end!) about a woman who feared a pregnancy diagnosis by her doctor so she mixed her urine with cow urine. The doctor declared her pregnant and when she explained what she had done, he declared that both she AND the cow were pregnant.
This cartoon is only funny in the way it gives medical historians the smug satisfaction of getting all the references. Additionally others will find it offensive and unprofessional that the physician insists on his diagnosis even in the light of significant new information. I fully expect an in-box full of angry letters from members of the Medieval Uroscopic Society after posting this.